blue baby vs infant

blue baby and infant both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue baby	Yes	No	No	No
infant	Yes	No	No	No

As nouns, infant is a hypernym of blue baby; that is, infant is a word with a broader meaning than blue baby:

blue baby: an infant born with a bluish color; usually has a defective heart
infant: a very young child (birth to 1 year) who has not yet begun to walk or talk

Other hypernyms of blue baby include babe, baby.

blue baby (noun)	infant (noun)
an infant born with a bluish color; usually has a defective heart	a very young child (birth to 1 year) who has not yet begun to walk or talk